Sauté Aromatics: Start by adding the butter and diced onion to your Instant Pot. Use the 'Sauté' function and cook until the onion softens, about 3-5 minutes. Stir in the minced garlic for about a minute, then press 'Cancel' to turn off the sauté mode.
Combine Ingredients: Next, add the elbow macaroni, diced ham, and water to the pot. Give it a quick stir to combine everything.
Pressure Cook: Secure the lid on your Instant Pot and set the vent to the sealed position. Cook on high pressure for just 4 minutes.
Release Pressure: Once the cooking cycle is complete, allow a natural pressure release for 5 minutes, then carefully perform a quick release of any remaining pressure.
Stir in Cheese: Open the lid and stir in the sour cream, Swiss cheese, and 2 cups of the cheddar cheese until they are beautifully melted and create a creamy sauce. It might seem a little soupy at first, but it will thicken.
Final Melt & Serve: Sprinkle the remaining 1 cup of cheddar cheese over the top of the macaroni. Place the lid back on for a few minutes to let this final layer of cheese melt completely. Remove the lid, let it stand for a moment to thicken, then season with salt and pepper to your liking. Serve this comforting, easy meal warm!